High voltage flashover prevention system



April 3, 1962 J. J. ROSE HIGH VOLTAGE FLASHOVER PREVENTION SYSTEM Filed Nov. 24, 1959 3 Sheets-Sheet 1 motmomiou INVENTOR.

JOHN J. OSE BYLUp-u' ANT April 3, 1962 J. J. ROSE HIGH VOLTAGE FLASHOVER PREVENTION SYSTEM Filed Nov. 24, 1959 3 SheetsSheet 2 all"! A WATTOM AGiJT April 3, 1962 J. J. ROSE HIGH VOLTAGE FLASHOVER PREVENTION SYSTEM Filed Nov. 24, 1959 s Sheets-Sheet a INVENTOR.

JOHN ROSE MORNEY AGE 3,027,718 VGLTAGE FLASHOVER PREVENTION SYSTEM John 3. Rose, 318 Deliwood Ave, Dayton, Ohio Filed Nov. 24, 195%, Ser. No. 855,246 4 Ciaims. (Cl. all-39.82) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to an improvement in high voltage ignition systems that use an igniter plug and which are subjected to high temperature and high altitude conditions, such as exist in systems for turbojet engines.

One object of the invention is to provide an ignition ystem for use at high temperature and high altitude which eliminates the problems of flashover at the terminal con nections of the igniter plug.

Another object is to provide an ignition system for use at high temperature and high altitude which make the use of electrical seals unnecessary.

These and other objectswill be more fully understood from the following detailed description taken with the drawing wherein:

FIG. 1 shows a turbojet engine with which the ignition system of the invention might be used.

FIG. 2 shows a prior art plug which is used in high voltage, high altitude ignition systems.

FIG. 3 shows an ignition system modified according to this invention.

FIG. 4 shows a modified seal used with the device of FIG. 3.

The ionizing voltage for the igniter plug gap may attain 25 kilovolts which presents a high altitude flashover problem in the terminal well at both ends of the ignition cable.

Presently the terminals are electrically sealed to prevent flashover, however, when temperatures exceeding 500 F. are present, deterioration of the sealing materials permits flashovers to occur at high altitudes.

According to Paschens law the sparkling potential of a gas is a function only of the product of the sparking distance and the pressure of the gas, so that if the product of sparking distance and pressure for any gas remains constant, the sparking potential will remain constant. In the igniter shown in FIG. 2 the sparking gap in the terminal is about ten times the length of the firing gap. Thus, if the pressure is kept substantially the same in these gaps, the firing potential in the terminals will be about ten times that in the firing gap and the firing gap will break down first. To attempt to prepressurize the system would require the whole system to be hermetically sealed which would be very costly if not impossible. According to this invention a passageway is provided through the igniter plug wall which extends into the compressor air discharge area so that pressure is supplied continuously and directly from the compressor to the terminal wells at both ends of ignition cable to maintain the pressure within the terminal wells approximately equal to that at the firing gap. This not only eliminates flashover but also makes the use of electrical seals unnecessary which simplifies the system.

Referring more particularly to FIG. 1 of the drawing, reference numeral refers to a portion of a turbojet engine having a combustion chamber 11. Air from the compressor, not shown, flows through the compressor chamber 12. An igniter plug 13 extends through the compressor chamber 12 into the combustion chamber 11. The firing gap 14, shown in greater detail in FIG. 2,

Patent 6 well.

is located within the combustion chamber. A compositor 15 produces the high voltage which is applied to the ignite-r plug 13 by means of shielded connector 16. The connector 16 is connected to the igniter plug in the manner shown in FIG. 3. An ignition unit 18, shownin FIG. 3, is connected to terminal 17 of compositor 15. Reference 44 shows the path of the air from the compressor to the plug and compositor. In the prior art, igniter plug of FIG. 2, a terminal 20, extends into terminal well 21 and the terminal is electrically sealed by means of a silicon rubber washer 22. This washer fits tightly around connector wire 23 and is urged against the top of the terminal insulator 25 and the terminal well 21 by means of a washer 26 and spring 27 and thus electrically seals the The firing gap 14 is across insulator 31 between electrodes 32 and 33. Electrode 33 consists of a portion of the outer casing of the igniter plug. The inner electrode 32 is connected to the connector Wire 23 by means of terminal means 34 and 35. The terminal at the compositor is identical to that shown in the igniter plug of FIG. 2. When systems of this type are used at high altitude and high temperature fiashover occurs due to deterioration of the silicon rubber Washer 22.

The terminals are modified according to this invention in the manner shown in FIG. 3 wherein parts like those shown in FIG. 2 are given like reference numerals. A small opening '41 is cut in the outer casing of the igniter plug in a portion of the plug which extends into the compressor chamber 12. Gaskets 42 and 43 are cut in the manner shown at 48 in FIG. 4 to permit the pressure from the compressor to be applied to the terminal wells at both ends of the connector 16, along the path shown by the dotted line 44. It can be seen that the length of gaps 45 at both ends of connector 16 are much greater than the gap 46 so that with the pressure approximately equal in all of these gaps, gap 46 will break down long before gaps 45.

There is thus provided an ignition system for use at high temperautre and high altitude which eliminates the problem of fiashover at the terminal connections.

While one specific embodiment has been described in some detail it is obvious that numerous changes may be made without departing from the general principles and scope of the invention.

I claim:

1. In a high voltage ignition system for a turbojet engine of the type having a compressor chamber and a combustion chamber wherein the ignition unit is connected to an igniter plug through a compositor unit and a substantially sealed connection having terminal means at the ends thereof adapted to engage terminal wells in the compositor unit and igniter plug, the igniter plug having an outer casing adapted to extend through the compression chamber into the combustion chamber, comprising: an opening in said outer casing in the rigion adapted to extend through said compressor and a passageway from said opening to said terminal wells to thereby maintain equalization of pressure within said terminal wells and said compressor chamber under substantially static flow condi tions.

2. In a high voltage ignition system for a turbojet engine of the type having a compressor chamber and a combustion chamber, comprising; an ignition unit, a compositor unit connected to said ignition unit, an igniter plug, said compositor unit and said igniter plug each having a terminal well of insulating material therein, a shielded connection between said compositor unit and said igniter plug, said shielded connection having terminal means located within said terminal wells for connecting said compositor unit to said igniter plug, said igniter plug having an outer casing with a portion adapted to extend through said compressor chamber into said combustion chamber, an opening in said outer casing in the region adapted to extend through said compressor, and a passageway from said opening to said terminal wells, to thereby maintain the pressure within said terminal Wells substantially equal to the pressure in said compressor chamher.

3. An igniter plug for use in a high voltage ignition system of an engine of the type having a compressor chamber and a combustion chamber, comprising; an outer casing having a portion adapted to extend through said compressor chamber into said combustion chamber which serves as an outer electrode, an inner electrode which together with said outer electrode constitutes a firing gap, means for spacing said outer electrode from said inner electrode to thereby provide a firing gap, a terminal well with a depth substantially greater than the width of said firing gap within said outer casing at the end remote from said firing gap, an opening in said outer casing in the region adapted to extend through said cornpressor chamber, and a passageway from said opening to said terminal well.

4. In a high voltage ignition system for a turbojet engine of the type having a compressor chamber and a combustion chamber, comprising; an ignition unit, a compositor unit connected to said ignition unit, an igniter plug, said compositor unit and said igniter plug each having a terminal well of insulating material therein, a

shielded connection between said compositor unit and said igniter plug, said shielded connection having terminal means located within said terminal wells for connecting said compositor to said igniter plug, said igniter plug having an outer casing with a portion adapted to extend through said compressor chamber into said combustion chamber which serves as an outer electrode, an inner electrode which together with said outer electrode constitutes a firing gap, ceramic insulating spacer means located between said outer electrode and said inner electrode, said insulating means having said igniter plug terminal well located at the end thereof opposite said inner electrode, the depth of said wells being substantially greater than the width of said firing gap, an opening in said outer casing in the region adapted to extend through said compressor chamber, and a passageway from said opening to said terminal wells, to thereby maintain the pressure in said terminal Wells substantially equal to the pressure in said firing gap.

References Cited in the file of this patent UNITED STATES PATENTS 2,195,025 Couzinet Mar. 26, 1940 2,286,233 Scott June 16, 1942 2,310,575 Cattaneo Feb. 9, 1943 2,493,743 Benson Jan. 10, 1950 2,651,298 Brinson Sept. 8, 1953 

